The jet of Mrk 501 from The jet of Mrk 501 from millions of Schwarzschild radii millions of Schwarzschild radii

down to a few hundredsdown to a few hundreds

Marcello GirolettiMarcello GirolettiINAF Istituto di RadioastronomiaINAF Istituto di Radioastronomia

andandG. Giovannini, G. Taylor, B. CottonG. Giovannini, G. Taylor, B. Cotton

M.Perez Torres, P. Edwards, M. ChiabergeM.Perez Torres, P. Edwards, M. Chiaberge

Outline

IntroductionObservations & results

− High sensitivity: HSA− High resolution: VSOP1 & Global mm-VLBI Array

Open questions & perspectivesSummary

Markarian 501

BL Lac @ z = 0.034, HBL high energy:

− detected by EGRET and TeV Cherenkov

− highly active/variable− SSC models require high

(>10) Doppler factor radio

− S5 GHz = 1 Jy

− VLA: two sided− pc scales: one sided-jet,

twisting

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High Sensitivity Array (HSA)

The High Sensitivity Array:− VLBA (10x25m)− phased VLA (27x25m)− Arecibo (300m)− Green Bank (110m)− Effelsberg (100m)− 7x more sensitive than the

VLBA alone! Our observations:

− 8 hrs, 1.6 GHz (optically thin regime), large recording rate (256 Mbps)

− final rms noise: 25 Jy beam-1

Increase in sensitivty means…

1. VLBA snapshot2. Deep Space

VLBI3. Our new data:

not only a beautiful image but also rich of information

4. 3000% increase in number of pixels above noise

HSA: the jet velocity structure

transverse: − slice at 100 mas from core

is limb brightened− two velocity regime?

radial− SED/high energy emission

require high velocity jet (Γ=15, θ=4o (δ15) in the -ray region (< 0.02 pc)

− one-sided jet confirms relativistic velocity out to 1” from the core

− probably larger viewing angle (=10o-15o) and slower velocity (Γ=10, δ2.6)

HSA: the magnetic field structure

magnetic field structure− polarized intensity as

high as 100 mJy/beam− organized magnetic field− B stratified in the inner

jet, perpendicular to jet axis after the bend

− from adiabatic model: consistent with polarization, requires high initial velocity

helix: intriguing but inconsistent with predictions

high res by long baselines: Space VLBI

compact structures are resolved in higher resolution images

no proper motion over 9 epochs− similar to other TeV blazars

limb brightening clearly revealed by VSOP

− interpreted in terms of velocity structure: fast inner spine, slower external shear

− intermediate viewing angle− important for theoretical jet models− where is its origin?

need even better resolution!

Giroletti et al. 2004

high res by higher frequency: mm-VLBI

VLBA ok @43 GHz, not adequate @86

the Global mm VLBI array operates @3mm with larger dishes and longer baselines (VLBA+IRAM telescopes+Eb+On+Mh)

resolution ~0.05 mas still not very sensitve (0.1-

0.4 Jy)... ...but enough to detect

Mrk501

GMVA obs of Mrk 501: results

resolution ~110 x 40 as rms ~ 1.5 mJy/beam core unresolved at 86 GHz

− size smaller than 0.03 pc (gaussian fit)

− MBH=109 Msun, 1 RS=10-4 pc− radius ~ 300 RS

− TB > 4 x 109 K St=150 mJy, Sc=45 mJy

− limb brightening in core region?

− 10 mJy component @0.73 mas, PA 172o

cleaning, model fitting, self-calibration difficult

GMVA obs of Mrk 501: results

steep high frequency spectrum, turnover @ ~8 GHz

− magnetic field in the range 0.01 – 0.03 G

− structure within the “core” − starting velocity and acceleration?− constraints from -ray emission?

GLAST, AGILE jet structure

− did we eventually find a "real" jet knot?

− orientation, limb brightening seem to be in agreement with VLBA at 43 GHz

Marscher et al. 2002

VLBI obs of Mrk 501: open questions

1) is limb brightened structure real?− need better sensitivity and (u,v) coverage

2) is spectrum really optically thin?− need more accurate amplitude calibration and

(possibly) resolution

3) what is the magnetic field structure?− need sensitivity and polarimetry

4) what do other blazars look like?− need sensitivity and ease of use

VLBI observations: perspectives

sub-parsec scale structure:1. new mm-VLBI observations just obtained for

Mrk501 (8/5/08)

2. mm-VLBI observations for 4 more blazars to take place next session (10/08)

3. VSOP2 (launch 2012) will be the key…

connection to high-energy activity:− waiting for GLAST, AGILE results− Medicina and Noto radio telescopes participated

in recent multi- campaign

take home notes

mrk 501 interesting source− twisting jet, one vs. two sided

structure, TeV source

high resolution and sensitivity essential

− HSA: perpendicular B field− VSOP1 successful: limb brightening,

resolved components− mm-VLBI detection ok, but open

questions remain

VSOP2, GLAST needed− also for many more sources!